The humanized anti-α4 integrin monoclonal antibody natalizumab has proven to be very effective in patients with highly active relapsing-remitting multiple sclerosis (MS), but harbors the risk of progressive multifocal leukoencephalopathy (PML). Recently, new therapeutic options have become available for patients with high risk of developing PML while on natalizumab treatment. One of these new therapeutics is the oral synthetic purine analogue cladribine. In order to determine whether therapy with cladribine is effective and safe in patients with MS who previously had been treated with natalizumab, we analyzed clinical, radiological, and laboratory data of 17 patients whose disease modifying treatment (DMT) was switched from natalizumab to cladribine.

A total of 17 patients with prior natalizumab treatment were switched to a DMT with cladribine because of a John Cunningham virus (JCV) antibody index above 1.5 (N = 13), ongoing disease activity (N = 6), magnetic resonance imaging (MRI) disease activity (N = 4), or patients preference (N = 2). A chart review and follow up of those patients was performed. In addition to MRI and laboratory data, clinical data regarding MS relapses and disease progression or possible adverse events were analyzed.

The median duration of cladribine treatment between February 2018 and April 2019 amounted to 9.7 months (range: 1.5–15 months). None of our 17 patients presented with a clinical relapse. Only two patients showed a new T2 lesion on brain MRI, but without any signs of PML. As expected, reduction of lymphocyte count was frequent in cladribine-treated patients, but only four patients exhibited lymphopenia grade 2 (500–800/µl).

In our cohort the switch from natalizumab to cladribine treatment was effective and safe. So far, no serious adverse events other than lymphopenia have been observed, especially no cases of PML.